High reserve alkalinity anti-freeze



fi ibi Patented July 24, 1%52 fine 3,046,229 IHGH RESERVE ALKALINTTY ANTI-FREEZE John C. Cessna, Parma, and Robert E. Mallonee, Cleveland, Ohio, assignors to Union Carbide Corporation, a

This invention relates to the inhibition of aluminum corrosion in glycol base aqueous anti-freeze solutions and more particularly, it relates'to ethylene glycol base anti-freeze solutions which contain alkaline earth metal borates in a sufficient amount to substantially inhibit aluminum corrosion.

It is well known that automotive coolant systems will suffer metallic corrosion in the presence of ethylene glycol-Water anti-freeze solutions unless these solutions contain certain materials which act as corrosion inhibitors. Protection must be extended not only to the cast iron engine block, to prevent serious rust clogging of small coolant passages, but also to solder, copper, brass, and aluminum metal surfaces, all of which are found in modern automotive systems, to prevent radiator perforations and subsequent leakage and loss of the anti-freeze solution and malfunction of other cooling system components.

At the present time, the trend is to use more and more aluminum in cooling systems and correspondingly it is becoming increasingly important to find a successful inhibitor to prevent corrosion of aluminum surfaces.

A number of inhibitors have been employed in the art, either alone or in combination, in commercial ethylene glycol base anti-freeze solutions including borax, sodium metaborate, calcium borate, magnesium borate, nitrites, the sodium salt of mercaptobenzothiazole, phosphates, amines and soluble oils. Of these, borax is the most commonly used. Test results show that borax-inhibited anti-freeze formulas give very poor aluminum protection and furthermore none of the inhibitors give completely satisfactory aluminum protection when used in the manner set forth by the prior art.

The principal object of the invention is to provide a glycol base anti-freeze solution which will substantially inhibit corrosion'of all metals commonly found in automotive cooling systems. A more specific object of the invention is to provide a glycol base anti-freeze solution having a high reserve alkalinity and which is substantially non-corrosive to aluminum.

A still more specific object of the invention is to provide a glycol base anti-freeze solution which will substantially inhibit aluminum corrosion by having contained therein alkaline earth metal borates in sufiicient quantities.

An even more specific object of the invention is to provide a glycol base anti-freeze solution which will substantially inhibit aluminum corrosion by having contained therein calcium borate in a high concentration.

It has unexpectedly been discovered that alkaline earth metal borates, and in particular calcium borate inhibited glycol base anti-freeze solutions having a high reserve alkalinity successfully inhibit aluminum corrosion to a much greater degree and for a longer duration than heretofore has been possible, and accordingly the invention comprises contacting the metals found in cooling systems with such anti-freeze solutions.

The term reserve alkalinity, as used in the specification and the appended claims, is a measure of the cation concentration of a freshly prepared anti-freeze formula, and is defined as the number of milliliters of one-tenth normal hydrochloric acid required to titrate one hundredmilliliters of thirty-three percent aqueous anti-freeze solution to a pH of 5.5. The term high reserve alkalinity in the case of calcium borate inhibited solutions, refers to glycol base anti-freeze having a reserve alkalinity of 170 units or greater.

A commonly held view that an increase in inhibitor concentration will cause a decrease in metallic corrosion is not true for all metals. This is particularly the case for aluminum when using the alkali metal borates as inhibitors because increased reserve alkalinity in borax inhibited glycol base anti-freeze solutions increases aluminum corrosion. Similarly, at low reserve alkalinity (below units) increased calcium borate concentration increases aluminum corrosion. However, at reserve alkalinity values above 170 units, calcium borate inhibited glycol base anti-freeze solutions show remarkably low aluminum corrosion rates. Other metals commonly found in cooling systems show the expected increased protection in high reserve alkalinity calcium borate solutions.

Studies of inorganic borate-ethylene glycol solutions in water have shown that metal protection, especially with regard to aluminum, is dependent upon three factors: (1) concentration of the inhibitor, (2) anion-cation ratio, and (3) the type of cation. For protection of metals other than aluminum used in cooling systems, reserve alkalinity of 200 or thereabouts is good, but for aluminum protection reserve alkalinity with conventional alkali metal borate inhibitors should not exceed about 55 units. Aluminum corrosion, particularly in the reserve alkalinity range of 100 to 200 is severe in the presence of alkali metal borates taken from periodic group IA such as sodium, lithium, and potassium borates, andaluminum corrosion increases with increasing reserve alkalinity. On the contrary, it has been discovered that alkaline earth borates taken from periodic group HA such as magnesium, calcium, strontium and barium borates inhibit so satisfactorily that when, in particlar, the calcium borate reserve alkalinity is above 170 units and the anion-cation ratio is in the range of 8 to 1 to 5 to 1 mole ratio of boric acid to metal calcium oxide, aluminum corrosion is frequently nil, and moreover, the higher the calcium borate reserve alkalinity between 170 and 750 units the less aluminum corrosion there is. It is this revolutionary and completely unexpected and unobvious discovery that forms the basis for the invention.

A typical calcium borate anti-freeze formula having a reserve alkalinity of 200 units and 76 grams of boric acid per liter of solution may be prepared in 3 liter quan tities by dissolving 228 grams of boric acid and 51 grams of calcium oxide in 3000 milliliters of ethylene glycol. This solution would have a 4 to 1 mole ratio of anion to cation. The performance of aqueous solutions of this anti-freeze is illustrated in Table I below. Representative .data for boraX inhibited anti-freeze solutions is also shown for comparative purposes. The tests which gave the results listed in Table I were carried out by placing aluminum plates having 4.5 square inches of surface area in the indicated anti-freeze solutions in the presence of rust for hours, at a temperature of 77 C. and the weight losses are recorded as the number of milligrams of weight lost and the formula number refers to the number of reserve alkalinity units.

TABLE I Aluminum Weight Losses in Prerusted Beaker Tests Formula: Weight losses Calcium borate 200 8, 0, 1 Sodium borate 200 125, 87, 121

The above table clearly shows the unexpected results obtained from the use of the anti-freeze solution of the subject invention. In order ot test the solution further, prerusted engine dynamometer tests were run employing calcium borate inhibited glycol base anti-freeze solutions having varying reserve alkalinity and the aluminum Weight losses in milligrams per 4.5 square inches of surface area were recorded. When a calcium borate inhibited glycol base anti-freeze solution having a reserve alkalinity of 55 units was tested a weight loss of 160 milligrams was recorded. When a solution having a reserve alkalinity of 100 units was tested the weight loss increased as expected and a loss of 342 milligrams was recorded. Finally, a solution havingthe preferred reserve alkalinity of 200 units was tested and the aluminum weight loss did not increase as would be expected from the prior art, but on the contrary was greatly decreased and a loss of only 15 milligrams was recorded.

For best results, the reserve alkalinity range should be greater than 170 units and the mole ratio of boric acid to calcium oxide should be 3.3 to 1 or greater. A reserve alkalinity of 170 is approximately the minimum high reserve alkalinity level to give satisfactory protection in automotive cooling systems containing aluminum. Aluminum corrosion protection is least at approximately 100 reserve alkalinity units. Prior to this discovery successfully marketed alkaline anti-freeze solutions have been limited to a reserve alkalinity of approximately 55 units.

By the use of the anti-freeze solutions of the subject invention it will now be possible to increase the protection of all the metals commonly found in automotive cooling systems including aluminum due to the discovery that alkaline earth metal borates having a reserve alkalinity of 170 units or higher successfully inhibits the corrosion of aluminum.

What is claimed is:

1. An ethylene glycol base anti-freeze solution having dissolved therein boric acid and a metallic oxide chosen from the group consisting of magnesium oxide, calcium oxide, strontium oxide and barium oxide, said boric acid and said selected metallic oxide being present in suflicient quantities to give a reserve alkalinity of at least 170 units to said solution; said reserve alkalinity being the measure of the cation concentration of a freshly prepared anti-freeze formula and defined as the number of milliliters of one-tenth normal hydrochloric acid required to titrate one-hundred milliliters of thirty-three percent aqueous anti-freeze to a pH of 5.5.

2. An ethylene glycol base anti-freeze solution having dissolved therein boric acid and calcium oxide in suflicient quantities to give a reserve alkalinity of at least 170 units to said solution; said reserve alkalinity being the measure of the cation concentration of 'a freshly prepared anti-freeze formula and defined as the number of milliliters of one-tenth normal hydrochloric acid required to titrate one-hundred milliliters of thirty-three percent aqueous anti-freeze to a pH of 5.5.

3. The anti-freeze solution of claim 2 wherein the mole ratio of anion to cation is between about 3 to l and 5 to 1.

4. The anti-freeze solution of claim 2 wherein said reserve alkalinity is at least 200 units and the mole ratio of anion to cation is about 4 to 1.

5. A calcium borate inhibited ethylene glycol base anti-freeze solution having a reserve alkalinity of at least 170 units, said reserve alkalinity being the measure of the cation concentration of a freshly prepared anti-freeze formula and defined as the number of milliliters onetenth normal hydrochloric acid required to titrate one hundred milliliters of thirty-three percent aqueous antifreeze to a pH of 5.5

References Cited in the file of this patent UNITED STATES PATENTS 2,765,278 Holter et al. Oct. 2, 1956 2,803,603 Meighen Aug. 20, 1957 2,803,604 Meighen Aug. 20, 1957 2,834,735 Woodle et al. May 13, 1958 

1. AN ETHYLENE GLYCOL BASE ANTI-FREEZE HAVING DISSOLVED THEREIN BORIC ACID AND A METALLIC OXIDE CHOSEN FROM THE GROUP CONSISTING OF MAGNESIUM OXIDE, CALCIUM OXIDE, STRONTIUM OXIDE AND BARIUM OXIDE, SAID BORIC ACID AND SAID SELECTED METALLIC OXIDE BEING PRESENT IN SUFFICIENT QUANTIES TO GIVE A RESERVE ALKALINITY OF AT LEAST 170 UNITS TO SAID SOLUTION; SAID RESERVE ALKALINITY BEING THE MEASURE OF THE CATION CONCENTRATION OF A FRESHLY PREPARED ANMTI-FREEZE FORMULA AND DEFINED AS THE NUMBER OF MILLILITERS OF ONE-TENTH NORMAL HYDROCHLORIC ACID REQUIRED TO TITRATE ONE-HUNDRED MILLILITERS OF THIRTY-THREE PERCENT AQUEOUS ANTI-FREEZE TO A PH OF 5.5. 